ATM kinase is a serine threonine kinase originally identified as the product of the gene mutated in ataxia telangiectasia. Ataxia telangiectasia is located on human chromosome 11q22-23 and codes for a large protein of about 350 kDa, which is characterized by the presence of a phosphatidylinositol (“PI”) 3-kinase-like serine/threonine kinase domain flanked by FRAP-ATM-TRRAP and FATC domains which modulate ATM kinase activity and function. ATM kinase has been identified as a major player of the DNA damage response elicited by double strand breaks. It primarily functions in S/G2/M cell cycle transitions and at collapsed replication forks to initiate cell cycle checkpoints, chromatin modification, HR repair and pro-survival signalling cascades in order to maintain cell integrity after DNA damage (Lavin, 2008).
ATM kinase signalling can be broadly divided into two categories: a canonical pathway, which signals together with the Mre11-Rad50-NBS1 complex from double strand breaks and activates the DNA damage checkpoint, and several non-canonical modes of activation, which are activated by other forms of cellular stress (Cremona et al., 2013).
ATM kinase is rapidly and robustly activated in response to double strand breaks and is reportedly able to phosphorylate in excess of 800 substrates (Matsuoka et al., 2007), coordinating multiple stress response pathways (Kurz and Lees Miller, 2004). ATM kinase is present predominantly in the nucleus of the cell in an inactive homodimeric form but autophosphorylates itself on Ser1981 upon sensing a DNA double strand break (canonical pathway), leading to dissociation to a monomer with full kinase activity (Bakkenist et al., 2003). This is a critical activation event, and ATM phospho-Ser1981 is therefore both a direct pharmacodynamic and patient selection biomarker for tumour pathway dependency.
ATM kinase responds to direct double strand breaks caused by common anti-cancer treatments such as ionising radiation and topoisomerase-II inhibitors (doxorubicin, etoposide) but also to topoisomerase-I inhibitors (for example irinotecan and topotecan) via single strand break to double strand break conversion during replication. ATM kinase inhibition can potentiate the activity of any these agents, and as a result ATM kinase inhibitors are expected to be of use in the treatment of cancer, for example as rational combination partners for existing therapies.
CN102372711A reports certain imidazo[4,5-c]quinolin-2-one compounds which are mentioned to be dual inhibitors of PI 3-kinase α and mammalian target of rapamycin (“mTOR”) kinase. Among the compounds reported in CN102372711A are the following:
